The present invention relates to an azetidinone derivative having the general formula (I): ##STR3## wherein R.sup.1 and R.sup.2 are hydrogen atom or a protective group and R.sup.3 is an alkyl group or hydrogen atom, a process for preparing the same, and a process for preparing an azetidinone derivative having the general formula (II): ##STR4## wherein R.sup.1, R.sup.2 and R.sup.3 are as above.
The azetidinone derivative (I) of the present invention can be converted into an important intermediate of 1.beta.-methylcarbapenem antibiotics by a selective reduction of the double bond (cf. the following Reference Examples). The 1.beta.-methylcarbapenem antibiotics show an excellent antibacterial activity against almost all kinds of bacteria including Psendomonas aeruginosa with much more powerful activity than that of known drugs and an excellent stability against .beta.-lactamase. Moreover, the 1.beta.-methylcarbapenem antibiotics also have a metabolic stability, which was not obtained in case of the carbapenem antibiotics, and thus are greatly expected to be the .beta.-lactam antibiotics of the fourth generation.
It is well known that .beta.-lactam compound having the general formula (II): ##STR5## wherein R.sup.1, R.sup.2 and R.sup.3 are as above, is a main intermediate for synthesizing 1.beta.-methylcarbapenem antibiotics. The conventional methods, however, cannot synthesize 1.beta. methyl group stereo-selectively and requires extremely troublesome procedures for separating stereoisomers (for example, D. H. Shih, F. Baker, L. Cama, and B. G. Christensen, Heterocycles, 21, 1 (1984); D. H. Shih, J. A. Fayter, L. D. Cama, B. G. Christensen, and J. Hirshfield, Tetrahedron Lett., 26, 583 (1985); D. H. Shir, L. Cama and B. G. Christensen, ibid., 26, 587 (1985); T. Shibata, K. Iino, T. Tanaka, T. Hashimoto, Y. Kameyama, and Y. Sugimura; ibid., 26, 4739 (1985)).
As a result of the present inventors' effort to solve the above-mentioned problem, it was found that the azetidinone derivative having the general formula (I) can be a very effective intermediate for synthesizing the above .beta.-lactam compound having the general formula (II).
It may be said that the industrial synthesis of the 1.beta.-methylcarbapenem antibiotics becomes easier by the present invention.